Mutualism in which ants must be present before plants produce food bodies

Abstract

Certain interactions between ants and plants can be classified as mutualisms^1–3, with benefit accruing to both members. The plant provides a source of energy, either as solid food or as nectar, and sometimes a domicile such as a hollow stem (or a stem capable of being made hollow by the ants) or hollow stipular thorns. The ants provide the plant with defence against herbivory and/or vine overgrowth. Whether the plant relies entirely or only in part on the ants for its defence, in relationships studied so far it always produces a source of food irrespective of the ants' presence. However, we report here that in the mutualistic relationship between the plant Piper cenocladum and the ant Pheidole bicornis, the production of food bodies is closely tied to the presence of the ants, so that when they are removed, production of food bodies nearly ceases and when ants reinvade the plant, production begins again. This is the first description of such a relationship in which the food tissue of the plant is induced by the insect.